Physicists discover “parallel loops” of spin currents in antiferromagnets

Physicists discover "parallel loops" of spin currents in antiferromagnets

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Left: An antiferromagnet can function as parallel electric circuits carrying spin currents Nel. Right: A tunnel junction based on antiferromagnets hosting spin currents Nel can be thought of as an electric circuit with the two ferromagnetic tunnel junctions connected in parallel. Credit: Shao Dingfu

A group of physicists from Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS) has revealed a secret of antiferromagnets, which could accelerate spintronics, a next-generation data storage and processing technology to overcome the bottleneck of modern digital electronics.

This discovery was reported in Physical Review Letters.

Spintronics is a rapidly developing field that uses the spin of electrons within magnetic materials to encode information. Spin-polarized electric currents play a central role in spintronics, due to their ability to manipulate and sense the directions of magnetic moments for writing and reading 1s and 0s. Currently, most spintronic devices are based on ferromagnets, where net magnetizations can efficiently rotate polarized electric currents.

Antiferromagnets, with opposite magnetic moments aligned alternately, are less studied but could hold the promise of even faster and smaller spintronic devices. However, antiferromagnets have zero net magnetization and are therefore commonly believed to carry only neutral spin currents that are useless for spintronics. Although antiferromagnets consist of two antiparallel aligned magnetic sublattices, their properties are believed to be “mediated” with respect to the sublattices making them independent of rotation.

Prof. Shao Ding-Fu, who led the team, has a different view on this research. He envisioned collinear antiferromagnets could function as “electric circuits” with the two magnetic sublattices connected in parallel. With this simple intuitive picture in mind, Prof. Shao and his collaborators theoretically predicted that magnetic sublattices could polarize the electric current locally, thus resulting in the spin-offset currents hidden within the globally spin-neutral current.

He dubbed these staggered spin currents “Nel spin currents” after Louis Nel, a Nobel laureate, who won the prize for his seminal work and discoveries regarding antiferromagnetism.

Spin Nel currents are a unique nature of antiferromagnets that has never been recognized. It is capable of generating useful spin-dependent properties that have previously been considered incompatible with antiferromagnets, such as a spin transfer torque and tunneling magnetoresistance in antiferromagnetic tunnel junctions, crucial for electrical writing and reading of information in antiferromagnetic spintronics .

‘Our work has uncovered a previously unexplored potential of antiferromagnetics and offered a simple solution to achieve efficient reading and writing for antiferromagnetic spintronics,’ said Prof. Shao Ding Fu.

More information:
Ding-Fu Shao et al, Nel Spin Currents in Antiferromagnets, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.216702

About the magazine:
Physical Review Letters

Provided by Hefei Institutes of Physical Science, Chinese Academy of Sciences

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